A power converter includes a self-driven circuit for appropriately turning ON and OFF a synchronous rectifier during the operating cycle of the power converter. Without the use of a smart controller coupled to the synchronous rectifier, the self-driven circuit turns ON the synchronous rectifier during the positive cycle of the power converter when the main switch is turned OFF, and the self-driven circuit turns OFF the synchronous rectifier during the negative cycle of the power converter when the main switch is turned ON. Unlike conventional self-driven circuits that include an auxiliary secondary winding for driving a synchronous rectifier, the self-driving circuitry of the present application does not include an auxiliary secondary winding.
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1. A power converter comprising: a. a transformer having a primary winding coupled to an input supply voltage and a secondary winding; b. a main switch coupled in series to the primary winding; c. a controller coupled to the main switch; d. a synchronous rectifier having a first terminal in direct electrical contact with a negative terminal of the secondary winding; e. an output capacitor having a first terminal in direct electrical contact with a positive terminal of the secondary winding and having a second terminal in direct electrical contact with a second terminal of the synchronous rectifier; f. a self-driven detection circuit coupled to the secondary winding, wherein the self-driven detection circuit is configured to turn ON when the main switch is OFF and is configured to turn OFF when the main switch is ON, further wherein the self-driven detection circuit comprises a first diode and a first transistor, wherein a cathode of the first diode is in direct electrical contact with the negative terminal of the secondary winding and the first terminal of the synchronous rectifier, an anode of the first diode is in direct electrical contact with a first terminal of the first transistor, and a second terminal of the first transistor is coupled to the positive terminal of the secondary winding; g. a first resistor having a first terminal in direct electrical contact with a third terminal of the first transistor; h. a second diode having a cathode an in direct electrical contact with a second terminal of the first resistor; i. a drive block coupled to the self-driven detection circuit and the synchronous rectifier, wherein the drive block is configured to turn ON when the self-driven detection circuit turns ON thereby turning ON the synchronous rectifier, and the drive block is configured to turn OFF when the self-driven detection circuit turns OFF thereby turning OFF the synchronous rectifier, further wherein the drive block comprises a third diode, a second transistor, a third transistor and a fourth transistor, an anode of the third diode in direct electrical contact with the positive terminal of the secondary winding, a cathode of the third diode in direct electrical contact with a first terminal of the second transistor, a first terminal of the third transistor in direct electrical contact with the fourth transistor, a second terminal of the second transistor in direct electrical contact with a second terminal of the third transistor and in direct electrical contact with a third terminal of the synchronous rectifier, a third terminal of the second transistor in direct electrical contact with a third terminal of the third transistor and in direct electrical contact with an anode of the second diode, and the fourth transistor in direct electrical contact with the second terminal of the synchronous rectifier and in direct electrical contact with ground.
A power converter efficiently regulates voltage using a transformer, a main switch controlled by a controller, and a synchronous rectifier. Instead of using an auxiliary winding, it features a self-driven detection circuit to control the rectifier's on/off state. This circuit consists of a diode and transistor network connected to the secondary winding. When the main switch is off, the diode conducts, turning on the first transistor. A resistor connects the first transistor's gate to a second diode. A drive block, composed of three additional diodes (one diode already mentioned) and three transistors, receives the signal from the detection circuit and controls the synchronous rectifier. The rectifier turns on when the main switch is off and turns off when the main switch is on, increasing efficiency by reducing losses. A capacitor provides output voltage smoothing. The 4th transistor is connected between the synchronous rectifier's terminal and ground.
2. The power converter of claim 1 wherein the transformer and the first diode are configured such that when the main switch is turned ON, the first diode is reverse biased thereby turning OFF the self-driven detection circuit and the drive block which turns OFF the synchronous rectifier.
Building upon the previous power converter description, the transformer and first diode's design ensures that the first diode is reverse biased when the main switch turns on. This reverse biasing action turns off the self-driven detection circuit and the drive block, which in turn shuts off the synchronous rectifier, preventing current flow and ensuring proper operation during that phase of the power conversion cycle. This eliminates the need for complex control circuitry, relying instead on the main switch's state.
3. The power converter of claim 2 wherein the first transistor is non-conducting when the first diode is reverse biased.
In the power converter described previously, when the main switch is turned ON, reverse biasing the first diode, the first transistor within the self-driven detection circuit becomes non-conducting. This means no current flows through the first transistor, disabling the rest of the self-driven circuit and preventing it from erroneously turning on the synchronous rectifier when it should be off. The transistor acts as a switch, and its state is directly linked to the state of the first diode.
4. The power converter of claim 3 wherein the first diode is reverse biased when the main switch is turned ON and the first diode is forward biased when the main switch is turned OFF.
Elaborating on the previous power converter description, the first diode's behavior is directly tied to the main switch. Specifically, the first diode is reverse biased (non-conducting) when the main switch is turned ON, effectively disabling the self-driven detection circuit. Conversely, the first diode becomes forward biased (conducting) when the main switch is turned OFF, enabling the self-driven detection circuit to potentially turn on the synchronous rectifier, depending on the circuit conditions.
5. The power converter of claim 3 wherein the self-driven detection circuit further comprises a second resistor, wherein a first terminal of the second resistor is in direct electrical contact with the positive terminal of the secondary winding, and a second terminal of the second resistor is in direct electrical contact with the second terminal of the first transistor.
Expanding upon the power converter described above, the self-driven detection circuit includes a second resistor. One end of this resistor connects directly to the positive terminal of the transformer's secondary winding. The other end of the second resistor connects directly to the drain terminal of the first transistor. This second resistor adds a control element to the first transistor within the self-driven detection circuit.
6. The power converter of claim 5 wherein the first transistor comprises a N-channel MOSFET, further wherein the first terminal of the first transistor is a source of the first transistor, the third terminal of the first transistor is a gate of the first transistor, and the second terminal of the first transistor is a drain of the first transistor.
Further specifying the power converter, the first transistor within the self-driven detection circuit is an N-channel MOSFET. In this configuration, the "first terminal" of the transistor is the source, the "third terminal" is the gate, and the "second terminal" is the drain. Therefore, the source is in direct electrical contact with the cathode of the first diode, the gate is connected to the first resistor, and the drain is connected to the positive terminal of the secondary winding via the second resistor.
7. The power converter of claim 6 wherein the second transistor is a P-channel MOSFET and the third transistor is a N-channel MOSFET.
Expanding on the previous power converter description, the second transistor within the drive block is a P-channel MOSFET, while the third transistor in the drive block is an N-channel MOSFET. These specific transistor types and polarities are crucial for the correct operation of the drive block and its ability to control the synchronous rectifier based on the output of the self-driven detection circuit.
8. The power converter of claim 7 wherein the fourth transistor is a NPN bi-polar junction transistor.
In addition to the P-channel MOSFET and N-channel MOSFET, the drive block of the power converter incorporates a fourth transistor, which is a NPN bipolar junction transistor (BJT). This BJT, in combination with the other transistors and diodes in the drive block, facilitates the precise and efficient switching of the synchronous rectifier in response to the self-driven detection circuit.
9. The power converter of claim 5 further comprises a third resistor, wherein a first terminal of the third resistor is in direct electrical contact with the positive terminal of the secondary winding, and a second terminal of the third resistor is in direct electrical contact with the third terminal of the second transistor, in direct electrical contact with the third terminal of the third transistor and in direct electrical contact with the anode of the second diode.
In the described power converter, a third resistor is added to the circuit. One end of this resistor is directly connected to the positive terminal of the secondary winding. The other end of the third resistor is connected to the gate of the second transistor, the gate of the third transistor, and the anode of the second diode. This resistor further biases the switching transistors in the drive block and controls their response to changes in the power converter's state.
10. The power converter of claim 1 wherein the second diode and the fourth transistor function as bias for proper operation of the third transistor in the linear region and the second transistor as a switch for turning ON and OFF the synchronous rectifier.
In the context of the power converter, the second diode and the fourth transistor function together to bias the third transistor for proper operation in the linear region, which is crucial for amplification. The second transistor operates as a switch, turning the synchronous rectifier ON and OFF based on the signal from the self-driven detection circuit, ensuring efficient power conversion by minimizing switching losses.
11. The power converter of claim 1 wherein a first terminal of the fourth transistor is in direct electrical contact with the second terminal of the synchronous rectifier and in direct electrical contact with ground, a second terminal of the fourth transistor is open, and a third terminal of the fourth transistor is in direct electrical contact with the first terminal of the third transistor.
Detailing the fourth transistor's connection in the power converter, one terminal is directly connected to both the second terminal of the synchronous rectifier and to ground. The second terminal of the fourth transistor is left unconnected ("open"). The third terminal is directly connected to the first terminal of the third transistor. This specific arrangement affects the rectifier's operation.
12. A power converter comprising: a. a transformer having a primary winding coupled to an input supply voltage and a secondary winding; b. a main switch coupled in series to the primary winding; c. a controller coupled to the main switch; d. a synchronous rectifier having a first terminal in direct electrical contact with a negative terminal of the secondary winding; e. an output capacitor having a first terminal in direct electrical contact with a positive terminal of the secondary winding and having a second terminal in direct electrical contact with a second terminal of the synchronous rectifier; f. a self-driven detection circuit coupled to the secondary winding, wherein the self-driven detection circuit comprises a first diode and a first transistor, wherein a cathode of the first diode is in direct electrical contact with the negative terminal of the secondary winding and the first terminal of the synchronous rectifier, an anode of the first diode is in direct electrical contact with a first terminal of the first transistor, and a second terminal of the first transistor is coupled to the positive terminal of the secondary winding, wherein the first transistor is configured to turn ON when the main switch is OFF and a secondary current through the secondary winding is greater than zero, and the first transistor is configured to turn OFF when the main switch is ON or when the main switch is OFF and the secondary current is zero; g. a first resistor having a first terminal in direct electrical contact with a third terminal of the first transistor; h. a second diode having a cathode in direct electrical contact with a second terminal of the first resistor; i. a drive block comprising a third diode, a second transistor, a third transistor and a fourth transistor, an anode of the third diode in direct electrical contact with the positive terminal of the secondary winding, a cathode of the third diode in direct electrical contact with a first terminal of the second transistor, a first terminal of the third transistor in direct electrical contact with the fourth transistor, a second terminal of the second transistor in direct electrical contact with a second terminal of the third transistor and in direct electrical contact with a third terminal of the synchronous rectifier, a third terminal of the second transistor in direct electrical contact with a third terminal of the third transistor and in direct electrical contact with an anode of the second diode, and the fourth transistor in direct electrical contact with the second terminal of the synchronous rectifier and in direct electrical contact with ground, further wherein the first transistor of the self-driven detection block is coupled to drive the second transistor of the drive block, and the second transistor is coupled to drive the synchronous rectifier such that the second transistor of the drive block is configured to turn ON when the first transistor of the self-driven detection circuit turns ON thereby turning ON the synchronous rectifier, and the second transistor of the drive block is configured to turn OFF when the first transistor of the self-driven detection circuit turns OFF thereby turning OFF the synchronous rectifier and disabling negative secondary current from flowing through the synchronous rectifier.
A power converter manages voltage with a transformer, a main switch, and a synchronous rectifier. It utilizes a self-driven detection circuit comprising a diode and transistor. The transistor turns ON when the main switch is OFF and current through the secondary winding is above zero, otherwise it remains OFF. A resistor connects to the transistor's gate, and another diode is connected to the resistor. A drive block (diodes, 3 transistors) drives the synchronous rectifier. The transistors switch ON or OFF the synchronous rectifier, preventing reverse current flow, triggered by first transistor of detection circuit. A capacitor regulates output voltage.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
August 7, 2015
May 23, 2017
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